Microsoft has announced it will end support for the on-premises version of Dynamics 365 Field Service in June 2022. It was said that "Dynamics 365 Field Services (on-premises)" that makes use of the older Field Service Mobile app built with Xamarin and that app will also be retired.
Kyle Young, Microsoft principal group program manager, "If you've already installed the on-premises version, it will still be available for your organization. However, new installations of Field Service (on-premises) will no longer be available from Microsoft. Also, the Field Service Mobile application that works with Field Service (on-premises) will be retired and no longer available after June 30, 2022."
On-prem customers will now have to migrate to the cloud app and this will need an upgrade to the latest online version of D365 Field Service. The transition will not require a licensing change.
Users need to remember that the download package to install Dynamics 365 Field Service (on-premises) will no longer be available after December 31, 2021. New installations of Field Service (on-premises) will no longer be available from Microsoft and this change does not apply to other Dynamics 365 on-premises apps.
In July 2015, Microsoft announced its plan to acquire the IP from FieldOne Systems that became Dynamics 365 Field Service. The product has undergone a range of updates in the meantime such as Teams integration, IoT partnerships, and alignment with Dynamics 365 Mixed Reality apps.